Add more documentation

knots/parallelism.scm

@@ -318,6 +318,12 @@ invocation of PROC finishes.  REPORT is passed the results for each
   (resource-pool     parallelism-limiter-resource-pool))
 
 (define* (make-parallelism-limiter limit #:key (name "unnamed"))
+  "Return a parallelism limiter that allows at most LIMIT concurrent
+fibers to execute within @code{with-parallelism-limiter} at the same
+time.  Further fibers block until a slot becomes free.
+
+@code{#:name} is a string used in log messages.  Defaults to
+@code{\"unnamed\"}."
   (make-parallelism-limiter-record
    (make-fixed-size-resource-pool
     (iota limit)
@@ -329,6 +335,9 @@ invocation of PROC finishes.  REPORT is passed the results for each
     parallelism-limiter)))
 
 (define* (call-with-parallelism-limiter parallelism-limiter thunk)
+  "Acquire a slot from PARALLELISM-LIMITER, call THUNK, release the
+slot, and return the values from THUNK.  Blocks if no slot is
+currently available."
   (call-with-resource-from-pool
       (parallelism-limiter-resource-pool parallelism-limiter)
     (lambda _

knots/promise.scm

@@ -41,12 +41,21 @@
   (evaluated-condition  fibers-promise-evaluated-condition))
 
 (define (fibers-delay thunk)
+  "Return a new fiber-aware promise that will evaluate THUNK when
+first forced.  THUNK is not called until @code{fibers-force} is
+called on the promise."
   (make-fibers-promise
    thunk
    (make-atomic-box #f)
    (make-condition)))
 
 (define (fibers-force fp)
+  "Force the fiber-aware promise FP, returning its values.
+
+The first call evaluates the promise's thunk.  Concurrent callers
+block on a condition variable until evaluation finishes, then receive
+the same result.  If the thunk raises an exception, the exception is
+stored and re-raised for all callers."
   (unless (fibers-promise? fp)
     (raise-exception
      (make-exception
@@ -108,6 +117,9 @@
 
 
 (define (fibers-delay/eager thunk)
+  "Return a new fiber-aware promise and immediately begin evaluating
+THUNK in a new fiber.  Exceptions during eager evaluation are silently
+discarded; they will be re-raised when @code{fibers-force} is called."
   (let ((promise (fibers-delay thunk)))
     (spawn-fiber
      (lambda ()
@@ -121,10 +133,15 @@
     promise))
 
 (define (fibers-promise-reset fp)
+  "Reset the fiber-aware promise FP so that the next call to
+@code{fibers-force} re-evaluates its thunk."
   (atomic-box-set! (fibers-promise-values-box fp)
                    #f))
 
 (define (fibers-promise-result-available? fp)
+  "Return @code{#t} if the fiber-aware promise FP has been evaluated
+(successfully or with an exception) and @code{#f} if evaluation has
+not yet started or is still in progress."
   (let ((val (atomic-box-ref (fibers-promise-values-box fp))))
     (not (or (eq? val #f)
              (eq? val 'started)))))

knots/queue.scm

@@ -25,6 +25,12 @@
   #:export (spawn-queueing-fiber))
 
 (define (spawn-queueing-fiber dest-channel)
+  "Spawn a fiber that serialises items onto DEST-CHANNEL in FIFO order.
+Returns a new input channel.
+
+Multiple producers can put items on the returned channel concurrently.
+The fiber buffers them locally and forwards them to DEST-CHANNEL one at
+a time, preserving arrival order."
   (define queue (make-q))
 
   (let ((queue-channel (make-channel)))

knots/thread-pool.scm

@@ -211,6 +211,52 @@ from there, or #f if that would be an empty string."
                                       (name "unnamed")
                                       (use-default-io-waiters? #t)
                                       default-checkout-timeout)
+  "Create a pool of SIZE threads started immediately.  Use
+@code{call-with-thread} to run a procedure in one of the threads.
+
+Optional keyword arguments:
+
+@table @code
+@item #:thread-initializer
+A thunk called once when each thread starts.  Its return value is
+passed as extra arguments to every procedure run in that thread.
+Defaults to @code{#f} (no extra arguments).
+
+@item #:thread-destructor
+A procedure called with the value returned by @code{#:thread-initializer}
+when a thread exits.  Defaults to @code{#f}.
+
+@item #:thread-lifetime
+Maximum number of procedures a thread will run before restarting (and
+re-running @code{#:thread-initializer}).  Defaults to @code{#f} (no
+limit).
+
+@item #:expire-on-exception?
+When @code{#t}, replace a thread after any unhandled exception.
+Defaults to @code{#f}.
+
+@item #:use-default-io-waiters?
+When @code{#t} (the default), each thread uses blocking I/O waiters so
+that port reads and writes block the thread rather than trying to
+suspend a fiber.
+
+@item #:name
+String used in thread names and log messages.  Defaults to
+@code{\"unnamed\"}.
+
+@item #:default-checkout-timeout
+Seconds to wait for a free thread slot before raising
+@code{&thread-pool-timeout-error}.  Defaults to @code{#f} (wait
+forever).
+
+@item #:delay-logger
+Called as @code{(delay-logger seconds proc)} with the time spent
+waiting for a thread to become available.
+
+@item #:duration-logger
+Called as @code{(duration-logger seconds proc)} after each procedure
+completes.
+@end table"
   (define channel
     (make-channel))
 
@@ -408,8 +454,34 @@ from there, or #f if that would be an empty string."
                            (use-default-io-waiters? #t)
                            default-checkout-timeout
                            default-max-waiters)
-  "Return a channel used to offload work to a dedicated thread.  ARGS are the
-arguments of the thread pool procedure."
+  "Create a dynamic thread pool with up to MAX-SIZE threads.  Use
+@code{call-with-thread} to run a procedure in one of the threads.
+
+Unlike @code{make-fixed-size-thread-pool}, threads are created on
+demand and may be reclaimed when idle (controlled by @code{#:min-size}
+and the resource pool's idle management).
+
+Accepts the same @code{#:thread-initializer}, @code{#:thread-destructor},
+@code{#:thread-lifetime}, @code{#:expire-on-exception?},
+@code{#:use-default-io-waiters?}, @code{#:name},
+@code{#:default-checkout-timeout}, @code{#:delay-logger}, and
+@code{#:duration-logger} arguments as @code{make-fixed-size-thread-pool},
+plus:
+
+@table @code
+@item #:min-size
+Minimum number of threads to keep alive.  Defaults to MAX-SIZE (i.e.@:
+the pool is pre-filled and never shrinks).
+
+@item #:scheduler
+Fibers scheduler for the pool's internal resource pool fiber.  Defaults
+to the current scheduler.
+
+@item #:default-max-waiters
+Maximum number of fibers that may queue waiting for a thread.  Raises
+@code{&thread-pool-timeout-error} when exceeded.  Defaults to
+@code{#f} (no limit).
+@end table"
   (define param
     (make-parameter #f))
 
@@ -444,8 +516,34 @@ arguments of the thread pool procedure."
                            channel
                            destroy-thread-on-exception?
                            (max-waiters 'default))
-  "Send PROC to the thread pool through CHANNEL.  Return the result of PROC.
-If already in the thread pool, call PROC immediately."
+  "Run PROC in THREAD-POOL and return its values, blocking until
+complete.  If called from within a thread that already belongs to
+THREAD-POOL, PROC is called directly in that thread.
+
+Optional keyword arguments:
+
+@table @code
+@item #:checkout-timeout
+Seconds to wait for a free thread before raising
+@code{&thread-pool-timeout-error}.  Defaults to the pool's
+@code{#:default-checkout-timeout}.
+
+@item #:max-waiters
+Maximum number of fibers that may queue waiting for a thread (for
+dynamic pools).  Defaults to the pool's @code{#:default-max-waiters}.
+
+@item #:destroy-thread-on-exception?
+When @code{#t}, destroy the thread after PROC raises an exception.
+Equivalent to per-call @code{#:expire-on-exception?}.  Defaults to
+@code{#f}.
+
+@item #:duration-logger
+Called as @code{(duration-logger seconds)} after PROC completes
+(whether or not it raised an exception).
+
+@item #:channel
+Override the channel used to communicate with the thread.
+@end table"
   (define (handle-proc fixed-size-thread-pool
                        reply-channel
                        start-time